Coordinative abilities of ligands which favour S,S chelation: copper(I) halide complexes of N,N'-diphenyldithiomalonamide. The crystal and molecular structure of bis(N,N'-diphenyldithiomalonamide)copper(I) iodide-methanol (2/1).

The spectroscopic (i.r. and n.m.r.) properties of [Cu(Hdpdma)2]X (Hdpdma = N,N′-diphenyldithiomalonamide; X = Cl, Br, or I) are discussed in the light of the structural results obtained for [Cu(Hdpdma)2]I·0.5MeOH. The compound crystallizes in the space group P1̄ of the triclinic system. In the unit cell two crystallographically independent [Cu(Hdpdma)2]+ cations, two iodine anions, and one methanol solvate molecule are present. The co-ordination around each copper atom is slightly distorted tetrahedral and involves four sulphur atoms belonging to two Hdpdma molecules, which act as bidentate neutral ligands and form two six-membered chelate rings. The i.r. study and the structural results, compared with those for other transition-metal complexes, permits some reasonable conclusions on the co-ordinative abilities of dithiomalonamides. The 1H and 13C n.m.r. results suggest that the same structural arrangement is maintained in solution.